1. Field of the Invention
The present invention relates to arc resistant cabinets for electrical equipment. More specifically, the invention relates to a panel defining a flap adapted to support weight from above, and to open in response to excessive pressure within the cabinet, thereby directing gases away from personnel.
2. Description of the Related Art
Electrical equipment such as circuit breakers are typically contained within arc resistant cabinets, intended to protect personnel working around the circuit breaker in the event of an electrical arc within the cabinet. Such an electrical arc would cause a sudden pressure increase inside the cabinet and localized overheating.
Presently available arc resistant cabinets typically include a frame having a hinged flap assembly. Such flaps are designed to support the weight of personnel working on top of the cabinet, but to open to relieve pressure inside the cabinet when an arc occurs. However, such gases may be deflected off the ceiling and wall of the room wherein the cabinet is located, down on to personnel working near the cabinet. Current and proposed safety standards require that the temperature of such gases be tested by placing highly flammable cotton indicators at a height of 2 meters around the perimeter of the cabinet, and these cotton indicators must not ignite when an internal arc occurs.
Accordingly, there is a need for an arc resistant cabinet having a means for directing high temperature, expanding gases exiting the cabinet away from locations where personnel are likely to be present. Additionally, there is a need for an arc resistant cabinet having a means for relieving pressure from high temperature, expanding gases while being easier and less expensive to produce than other arc resistant cabinets.
The preferred embodiment of the present invention is a pressure release panel for use with arc resistant cabinets. Such pressure relief panels are particularly useful for arc resistant cabinets containing electrical equipment, such as circuit breakers.
The pressure relief panel includes at least one flap defined by a plurality of cuts within the panel. Some preferred embodiments include multiple flaps. A support system is secured below each flap, being dimensioned and configured to prevent the flap from bending downward when pressure is applied to the top of the panel. One preferred support system includes a beam extending lengthwise along each cut.
A preferred and suggested method of making such a pressure relief panel includes providing a solid panel, cutting the panel at appropriate locations to define at least one flap, with one preferred cutting method being a laser, and securing the support system below the flaps. A preferred material for the panel is steel, with 14-gauge steel being suggested. Preferred methods of securing the support system below the flaps include bolting and welding the support system in place.
In use, such pressure relief panels will typically form the roof of an arc resistant cabinet, although they may be used at other locations inside the cabinet. Such cabinets are typically used to contain electrical equipment such as circuit breakers. When an arc occurs within a circuit breaker, the result is high pressure, high temperature expanding gases within the cabinet. Relieving the pressure inside the cabinet requires releasing these gases in a direction wherein the gases are not likely to cause injury to personnel working around the cabinet.
During normal operation of the circuit breaker, the flap will remain closed, and the support structure beneath the flap will permit personnel to walk over the panel and flap without causing the flap to collapse. When an electrical arc occurs, the high temperature, expanding gases will apply upward pressure to the pressure relief panels and flaps, causing the flaps to bend outward. The material type and thickness of the pressure relief panel will preferably be selected to ensure that such expanding gases are likely to push the flap into an approximately vertical position. The location of the pressure relief panel on the roof of the arc resistant cabinet, combined with the substantially vertical flaps, direct the expanding gas upward, and away from locations where personnel are likely to be present. The number, size and shape of the flaps can be selected to more specifically direct the flow of expanding gases out of the cabinet so that, by the time the gases reach the ceiling and walls of the room in which the cabinet is located, and are thereby directed back downward, the gases have cooled sufficiently so that they are unlikely to cause serious injury to personnel.
It is therefore an aspect of the present invention to provide a pressure relief panel for use with arc resistant cabinets.
It is another aspect of the present invention to provide a pressure relief panel capable of supporting the weight of personnel standing on the panel.
It is a further aspect of the present invention to provide a pressure relief panel wherein excess pressure underneath the panel will position a flap defined with the panel into an orientation wherein the flap directs expanding gases to locations where personnel are unlikely to be present.
It is another aspect of the present invention to provide a pressure relief panel wherein excess pressure below the panel pushes the flaps defined within the panel into a vertical orientation.
It is a further aspect of the present invention to provide a support structure beneath the flaps defined within a pressure relief panel for resisting downward movement of the flaps.
It is another aspect of the present invention to provide a pressure relief panel for arc resistant cabinets that is simple and inexpensive to manufacture while maintaining or exceeding the effectiveness of other pressure relief systems.